It is known that binder fibers may be blended with base or non-adhesive fibers to form a yarn or textile material and then the binder fiber may be melted, thereby adhering the base fibers together. See U.S. Pat. Nos. 2,880,112, 2,252,999, 3,877,214, 3,494,819 and 5,284,009, the entire subject matter of which is incorporated herein by reference. Typically, the binder fiber melts at temperatures sufficiently less than those at which the base fibers melt or begin softening, thereby allowing the base fibers to retain their physical properties while at the same time imparting the yarn or textile material with significantly improved properties (e.g., wearability, initial appearance, etc.).
Selection of binder fiber materials is important with regard to achieving improved properties in the resulting yarn or textile materials. Certain physical and chemical characteristics of binder materials are desirable, such as ability to adhere to the base fiber, ability to flow between base fibers under standard process conditions and/or ability to be unwound at high speeds (i.e., greater than 1,000 mpm). For example, U.S. Pat. No. 4,258,094, the entire subject matter of which is incorporated herein for reference, describes the use of an ethylene-vinyl acetate binder fiber with a base fiber to form melt bonded fabrics. U.S. Pat. No. 5,478,624, the entire subject matter of which in incorporated herein by reference, sets forth a synthetic yarn prepared from a blend of base fiber combined with a polyamide copolymer binder fiber. The yarn is utilized in a carpet and is heated to bond the base fibers together. U.S. Pat. No. 5,712,209, the entire subject matter of which is incorporated herein by reference, describes the use of polyethylene fibers as binder fibers in combination with base fibers that melt at temperatures above the melting ranges of the polyethylene fibers. The polyethylene fibers are melted to “lock” the base fibers in place, thereby producing a “dimensionally stable” structure.
Because binder fibers desirably melt at temperature ranges below those of base fibers, the binder material typically is limited to polymers having low melting temperature ranges (e.g., below about 200° C.). Many of these polymers possess a low propensity to crystallize (i.e., to form the stable inter- and intra-molecular associations with some degree of molecular periodicity that can be characterized by increased density, reduced shrinkage, a measurable endothermic heat of melting, and discrete x-ray scattering), if they do crystallize at all. Melt spinning of polymers having a low propensity to crystallize (i.e., to form a stable micromolecular crystalline structure) is quite difficult for a number of reasons, including low melt strength, quench difficulty and poor package formation. For example, various problems with melt spinning of low melting (e.g., below about 160° C.) polyamides is described in U.S. Pat. No. 4,225,699, the entire subject mater of which is incorporated herein by reference. The most significant problem to overcome lies in the “sticking” of filaments together and to the spin bobbin after being placed thereon. In a typical melt spinning process, after spinning the polymer into a multi-filament yarn, the yarn is quenched and then wound onto a spin bobbin. Subsequently the yarn is removed form the spin bobbin for further processing, such as drawing, annealing, finishing, inserting, etc. If the yarn is not easily withdrawn from the spin bobbin filament breakage occurs, resulting in a yarn that cannot be processed into satisfactory products.
In order to reduce sticking of melt spun filaments composed of low melting polymers, various processes and processing aids have been developed. For example, U.S. Pat. No. 3,901,989, the entire subject matter of which is incorporated herein by reference, describes a process for melt spinning a bicomponent fiber using a spin-draw technique that involves stretching or drawing of the multi-filament yarn after spinning and quenching. However, such spin-draw processes cannot be performed at high speed and are, thus, not commercially viable for commercial-type applications.
Another process for alleviating the sticking phenomenon relates to the quenching process. For example, improved cooling of the fiber during the quench step by increasing the velocity of the quench fluid is proposed in U.S. Pat. No. 5,411,693, the entire subject matter of which is incorporated herein by reference. However, the polymers utilized in this process melt at high temperature ranges and have a high propensity to crystallize. This process would not provide satisfactory results when spinning a low temperature melting polymer that has a low propensity to crystallize because such a filament's melt strength would be too low.
The aforementioned U.S. Pat. No. 4,225,699 does describe melt spinning of low melting polymers having a low propensity to crystallize. However, the process recited therein is conducted at low spinning speeds (i.e., 800 m/min.) and utilizes a spin draw technique, thereby rendering the processing commercially unacceptable for the reasons mentioned herein. Additionally, the unwinding tension of the filaments from the spin bobbin is quite high (i.e., above four grams) and is not suitable for existing commercial yarn insertion processes due to the propensity for breakage of the binder filaments.
There have been efforts to implement high speed melt spinning of various polymers into fibers. For example, U.S. Pat. No. 4,909,976, the entire subject matter of which is incorporated herein by reference, describes a process for high speed melt spinning of polyester using on-line zone cooling and heating. However, polyester is a high melting temperature (i.e., above 250° C.) polymer that exhibits a high propensity to crystallize (i.e., to form stable micromolecular structures of increased density) during the quenching process when spun at higher speeds. In contrast, polymers possessing a low melting temperature range with a low propensity to crystallize have not been melt spun at high speeds due to a low expectation of success because the low degree of stress induced crystallization expected from orienting the amorphous polymer chains in the filaments emerging from the quench zone. Such filaments typically must be further treated (i.e., cooled, drawn, annealed, etc.) in order to reduce sticking of the filaments placed on the spin bobbin, as mentioned in U.S. Pat. No. 4,225,699.
Accordingly, there is a need for a commercially viable high speed melt spinning process that produces acceptable non-sticking filaments composed of polymers possessing a low melting temperature range with a low propensity to crystallize.